Unexpected cracking found on critical Boeing 737 Next Generation part
Boeing 737-800 (Boeing file photo)
Boeing engineers and safety investigators are scrambling to find out how many Boeing 737NGs have cracked ‘pickle forks’ after finding several in the jets.
A pickle fork is the part that helps attach a plane’s fuselage to its wing structure. It helps manage the stress, torque and aerodynamic forces that bend the connection between the wings and the body of the jet.
Engineers design pickle forks to last the lifetime of the plane, more than 90,000 landings and takeoffs, a term known as “flight cycles” in the aviation industry, without developing cracks. There could be dire results if the pickle fork system on the jet fails in flight.
During a recent inspection, workers found a severely cracked pickle fork on a Boeing 737NG. The plane is relatively young, having logged approximately 35,000 flight cycles when the damage was found.
A retired Boeing engineer who asked to remain anonymous tells us, “It’s unusual to have a crack in the pickle fork. It’s not designed to crack that way at all. Period.”
He says it’s particularly concerning because it was found so early in the plane’s service.
Another source tells us Boeing quickly reported the issue with the single plane to the FAA last week, and now more planes with similar cracking have been found.
We’re told this is very much an ongoing investigation, and that it’s unclear whether or not this is a widespread issue.
Boeing confirmed to KOMO Friday that there is a cracking issue.
“Safety and quality are our top priorities. Boeing has notified the FAA and been in contact with 737NG operators about a cracking issue discovered on a small number of airplanes undergoing modifications. No in-service issues have been reported. Over the coming days, we will work closely with our customers to implement a recommended inspection plan for certain airplanes in the fleet. This issue does not affect any 737 MAX airplanes or the P-8 Poseidon,” a Boeing spokesperson wrote.
The FAA also confirmed the inspections, telling KOMO, “The FAA will require operators of certain Boeing 737NG jetliners to conduct inspections for structural cracks. Boeing notified the agency of the matter after it discovered the cracks while conducting modifications on a heavily used aircraft. Subsequent inspections uncovered similar cracks in a small number of additional planes. The FAA will instruct operators to conduct specific inspections, make any necessary repairs and to report their findings to the agency immediately.”
No one has been injured, and there have been no reports of issues on 737s that flew with the cracked equipment. It’s a near certainty that people flew aboard the jets with the cracked pickle forks before the issue was discovered.
We’re told this is an issue that is being taken seriously by the FAA and Boeing.
The pickle fork is essential to the safety of the plane and an in-flight failure could be catastrophic in the worst-case scenario.
A government source says that until the scope of the problem can be understood, it’s difficult to tell what corrective actions will need to be taken. It could be anything from visual inspections of all 737NGs, or more unlikely, a grounding of the planes for further inspections. Investigators are deeply concerned about the cracks developing so early on in a the plane’s lifespan.
Engineers say the inspection process itself is fairly straightforward and fast. 737NGs are the generation of models made prior to the 737 MAX. The 737NG is the model designated as 737-600, 737-700, 737-800, or 737-900. It started production 1996. The last one rolled off the factory floor this summer in Renton.
Light cracking is occasionally found in pickle forks, but it’s very unusual.
Engineers say fatigue cracking, once initiated, grows every flight.
If a slight crack is discovered during a routine inspection, engineers run a scenario for how much they expect it to grow under typical conditions, then re-inspect at prescribed intervals.
“A crack like this is similar to when you see a crack in a coffee cup handle,” the retired engineer tells us. “You can likely continue using the cup several more times, but there’s always a risk that handle will break off and hot coffee will wind up in your lap.”
Teams in Seattle and Washington, D.C are working on this. A source within the federal government says FAA inspectors were excited and happy to get the call from Boeing.
The source says they are “…elated that the bloodline of safety is alive at Boeing.” That same source worries about how economic concerns for Boeing impact safety.
Just this week, Boeing re-organized its management structure when it comes to safety. There’s even a committee on the Board of Directors now with direct oversight of safety.
Until the extent of the issue is discovered, it will be difficult to determine what maintenance crews will need to do. So far, there have been no government orders for mandatory inspections.
Boeing and the FAA will want to know why the pickle forks are cracking, and why it’s happening so early. We’re told it could be something as simple as a manufacturing flaw with a small number of planes and not something widespread.
This could be a pain for scheduled maintenance on planes. We’re told a “fix” to a pickle fork with extensive of cracking will require mechanics to remove and replace the pickle fork fitting. It stretches around 25% of the circumference of the fuselage. A Boeing 737 has four pickle forks.
The retired engineer tells KOMO the cracks were really surprising, used an expletive, then said, “This is not good news,” and added, “It’s really urgent to investigate.”
March 31, 2019
Matergenics presented six(6) technical papers at NACE 2019 Conference in Nashville, Tennessee:
1-Condition Assessment, Corrosion Risk Assessment, FEA Analysis Of Pack-out For Weathering Steel Transmission Structures
Dr. Zee WS paper C2019-13312
2-Corrosion Risk Assessment, Failure Analysis and Corrosion Mitigation for Aboveground Storage Tanks and Case Histories
Storage Tanks C2019-12826
3-CORROSION RISK ASSESSMENT AT ANCHOR SHAFTS OF TELECOMMUNICATION TOWERS
4-Coating Selection for Transmission and Distribution (T&D) Structures and Corrosion Maps
5-AC Interference Corrosion, Corrosive Soil, Corrosion Maps and Design Issues,
AC Interference C2019-12828
Dr. Zee presented a talk on corrosion risk assessment and corrosion mitigation strategies for stray current of galvanized fundations at NACE technical committee TEG 530X
Pittsburgh Post Gazet Posting
Don’t blame the metal, blame the human, and other lessons from a museum of materials failure
Pittsburgh Post Gazet Posting
ANYA LITVAK Pittsburgh Post-Gazette
DEC 4, 2018 9:00 Pm
Welcome to the museum of materials failure.
Your guide is Mehrooz Zamanzadeh.
You’ll notice you’re in an unconventional space — a conference room inside Matergenics Inc., his consulting company in a nondescript suburban office building in Robinson.
Perhaps that’s fitting — failure is ubiquitous and mundane, so no grand hall is necessary.
Also, all failure is a consequence of human error, Mr. Zamanzadeh will explain. You won’t read that in textbooks, “but this is the truth,” he said.
Please be advised that when you get inside the room, you may touch the jagged pipes and sawed-off pieces of corroded metal you see in the glass cases. But do be gentle: The museum is the accumulation of Mr. Zamanzadeh’s entire career in corrosion engineering and failure analysis.
He’s authored hundreds of detailed reports to companies that hire him to figure out what went wrong during a building collapse or a pipeline rupture, sending his findings into the ether.
Wouldn’t it be great to have a place to unite all that failure under one roof — stripped of company names, stripped of shame and liability and public relations anxieties?
Who does he envision visiting a one-room “museum” of grotesque metal? He says anyone who is curious about how stuff works.
“Why? Because these failures will be repeated.”
Goal-oriented visitors might consider a scavenger hunt. Here are some ideas to get you started.
- An engine that was shut down midflight.
- A piece of a purple pole from Disneyland.
- A tin-coated roof shingle from Thomas Jefferson’s original estate in Monticello, Va.
- A piece of a transmission tower that cracked a few years ago. It got cold and became brittle, just like the hull of the Titanic, Mr. Zamanzadeh can tell you. “It has happened many times in history, and it’s still happening.”
- Anodes that are used to pump electrons to buried metal as a way of preventing or slowing corrosion. Did you know an anode protects the Fred Rogers statue on the North Shore?
- An image of a pole from the parking lot of Pittsburgh International Airport that corroded and fell on a parked brand new BMW.
There are industries where failure has some sort of cachet: Tech entrepreneurs, especially those who’ve succeeded mightily, may grace their admirers with a TED Talk on the importance of failing.
Pittsburgh Post Gazet Posting
Aluminum oxygen cylinder at Matergenics Inc. Material Failure Museum Thursday Nov. 29, 2018, in Robinson.
For obvious reasons, that’s not the attitude of utilities and infrastructure firms.
If an app fails, it could take a financial and even mental toll on its users. If a bridge fails, it could cost lives. A horrific scene may be splashed across newspaper pages, but the root cause report likely won’t be.
In many cases, it will never be made public, Mr. Zamanzadeh said. How many times has he served as an expert witness with that expertise locked away in a civil settlement? How, then, will the rest of us know what not to do in the future?
Samuel West, who founded another Museum of Failure, which lovingly showcases consumer flops (e.g. Harley-Davidson eau de toilette), has charged that “very few companies and organizations learn from their mistakes.”
“We need to be better at learning from failure instead of sweeping things under the carpet and disassociating ourselves from failures,” Mr. West said.
For those of you who arrived in Robinson intending to visit Mr. West’s Museum of Failure, head about 4,100 miles east to Sweden.
To schedule a tour of Matergenics’ gallery of failure, call “Dr. Zee” at 412-952-9441 or email email@example.com.
Anya Litvak: firstname.lastname@example.org or 412-263-1455.
Fatigue Failure in Southwest Engine
Metal fatigue, metallurgy, ultrasonic inspection, and titanium alloys are in the news the past few days due to a catastrophic engine failure aboard a Southwest Airlines jet. Because ASM International is at the heart of the materials community, many of our members are employees of the organizations involved in investigating this incident and maximizing the safety of air travel and engine designs. We will continue to monitor this story and report on results once the investigation is complete. Included here is a short summary of events as well as links to other news stories and company statements.
On April 17, a crack on a fan blade led to the Southwest Airlines (SWA) disaster that killed one passenger and injured seven others. Because the crack was on an internal surface, it was not detectable by visual inspection, according to National Transportation Safety Board (NTSB) Chairman Robert Sumwalt. NTSB is now investigating why the fan blade came off the widely specified CFM56-7B engine, breaking the engine into pieces and sending metal parts into the 737 jet. The engine is manufactured by CFM International Inc., a joint venture between General Electric Co. and Safran SA.
NTSB investigators will also try to determine if the April 17 incident has any similarities to a 2016 engine failure that occurred on another SWA 737. The 2016 investigation is ongoing, but according to a statement on the NTSB website after the incident, evidence of a crack consistent with metal fatigue in that titanium alloy blade was discovered. In both incidents, the engines were CFM56-7Bs.
On April 17, Southwest announced it was conducting ultrasonic tests of all engines of the same vintage—tests that use ultrasonic sensors to detect cracks beneath the fan blade surface. Testing methods like this are able to detect most flaws before they lead to an explosive failure. However, they are not foolproof according to MIT metallurgy professor Cem Tasan, as quoted in a recent Bloomberg article. “The main problem is none of these techniques will give you a full picture of what is going on in the material,” says Tasan.
Also on April 17, the Federal Aviation Administration (FAA) ruled that Boeing 787 Dreamliners with Rolls-Royce engines could no longer be flown on lengthy over-water flights. This is due to the fact that cracks have developed on some engines used on the Boeing 787 and Boeing 767. An April 19 New York Times article states that the worry is that the flaws are part of a trend as manufacturers push to develop ever more powerful and complex machines. “We’ve gotten smarter,” said Richard Giannotti, an aerospace engineer. “We can design things to a very low margin with a lot of reliability data to back it up. But when we get to the ragged edge, it doesn’t take much for things to go wrong.” He said that in the past, engines were designed with an abundance of precaution. “They don’t do that anymore. They’re trying to whittle down every last bit of material, every bit of weight. Thrust is king.”
With regard to the investigation, a statement on the GE Aviation website reports that GE and Safran Aircraft Engines technicians (about 40 in total) are being deployed to support SWA’s accelerated inspection program related to the CFM56-7B engine, which powers the airline’s Next-Generation 737 fleet. Out of an abundance of caution, the ultrasonic inspections are being conducted on a population of fan blades. Working with Boeing, GE, and Safran Aircraft Engines, SWA expects the accelerated inspections to be completed over the next 30 days. Further, CFM has sent a team of technical representatives to the site to assist the NTSB in its investigation. CFM will support the NTSB and SWA in determining the cause of the accident. CFM and GE will make every resource necessary available to ensure support.
Please See ASM news to monitor this story and report on developments.
Reference Articles and Links
Metal Weakness in Southwest Jet Tests Limits of Safety Inspections (Bloomberg)
MATERGENICS NEWS LETTERS
MANUALS AND GUIDELINES
- Guide for Cathodic Protection of Transmission Line Structures, CEATI Report TLAM 3256, CEATI International (2015).
- Inspection and Mitigation of Underground Corrosion at Anchor Shafts of Telecommunication Towers, NACE Corrosion 2017 Conference, Paper No. 8898 (2017). [ Download PDF ]
- Galvanic Cathodic Protection for Power Transmission Tower Grillage Foundations, NACE Material Performance, Vol. 55, No. 12 (2016). [ Download PDF ] [ Read Online ]
- Cathodic Protection, Defective Coatings, Corrosion Pitting, Stress Corrosion Cracking, Soil Corrosivity Mapping and Corrosion Assessment in Aging Pipelines, NACE Corrosion Risk Management Conference, Paper No. 8727 (2016). [ Download PDF ]
- Numerical Simulation of Cathodic Protection Systems for Transmission Towers with Grillage-Type Foundations, NACE Corrosion 2016 Conference, Paper No. 7813 (2016). [ Download PDF ]
Fusion Bonded Epoxy Coatings (FBE) and Disbondment (7246)
By M. Zamanzadeh and Huiping Xu
Fusion Bonded Epoxy (FBE) coating has been used for corrosion protection of underground pipe lines since the 1960’s. FBE provides protection of pipeline under cathodic protection even though there may be dis-bondment or blistering. FBE does not shield cathodic protection current under normal conditions, a characteristic which likewise distinguishes FBE coating from all other coating. In this paper failure analysis methodology will be applied to the principal mechanisms by which FBE coatings fail during long term service; with specific application to case studies involving blistering.
The case studies apply standard failure analysis techniques to determine the primary causes and modes of failures. Solution in blistered areas, pH and presence of cations and chlorides on the surface and in the coating will provide evidence for surface contamination/dis-bondment mechanism. If AC interference or shielding is present, localized corrosion attack in blistered areas can be detected prior to deep penetration in to wall thickness by effective corrosion monitoring. This can be achieved by on-time monitoring of soil corrosivity and AC/DC interference by test coupons.
Keywords: Corrosion Protection, Pipeline, Coating, Fusion Bonded Epoxy Coatings (FBE), Blistering, Coating Failure Mechanism, Cathodic Protection, AC Interference, DC stray Current Corrosion,
Corrosion Risk Assessment and Failure Analysis in Industrial Water Systems – (7248)
By Mehrooz Zamanzadeh and Huiping Xu
Industrial water system components are at increasing risk of damage due to corrosion and metal loss as they get close to the end of their design life or if the system exhibits any of the following: accelerated corrosion, perforation, deposit build up (plugging), discoloration, and excessive attack due to corrosive bacteria.
The purpose of this paper is to provide failure analysis case histories on corrosivity, pitting tendency and the risk associated with corrosion activity in industrial water systems. Failure analysis methods, failure mechanisms, primary cause and sources of corrosion attack with recommendations are described at the end of each case history. Corrosion mitigation recommendations and risk ranking is based on many years of experiences and water system studies in industrial water systems.
Keywords: Corrosion Risk, Inspection, Failure Analysis, Industrial Water Systems, Corrosion Mitigation, Corrosivity, Pitting Corrosion.
Fatigue Failure Analysis Case Studies
By Mehrooz Zamanzadeh, Edward Larkin and Reza Mirshams
Fatigue fracture can occur in many components such as fasteners and tubular pole structures. In this paper, fatigue failure mechanisms have been described and the application of the principles for failure analysis for each case will be presented. Cyclic loading at stresses above the fatigue limit of the material can initiate cracks at the surface or at internal defects. Macroscopic and microscopic observations of fatigue crack initiation and approaches for characterization of fatigue failures have been described.
Two case studies present application of laboratory analysis techniques to determine primary causes and modes of failures.
Keywords: Fatigue Cracking, Fatigue Failure, Metallurgical Investigation, Fracture.
Cathodic Protection, Defective Coatings, Corrosion Pitting, Stress Corrosion Cracking and Soil Corrosivity Mapping and Corrosion Assessment in Aging Pipelines (Paper No. RISK16-8727)
By Mehrooz Zamanzadeh and Reza Mirshams
Pipelines are among the most common means used for transporting hazardous gases and liquids in the United States. However, underground pipelines are aging and are at risk of corrosion failure due to coating degradation, pitting corrosion and stress corrosion cracking. Those tasked with maintaining these pipelines require an in-depth understanding of the locations where these aging pipelines are at risk of localized corrosion attack and cracking. Corrosion failures in aging pipelines are either sudden catastrophic ruptures or gradual leaks due to localized corrosion. Many factors associated with these corrosion areas are coating failure, degradation, disbondment, blistering, delamination, mechanicalpressure and stress concentration, galvanic action, corrosive ions, the presence of moisture, corrosive soils, AC interference, inadequate cathodic protection and shielding.
These areas have a much higher statistical probability of catastrophic failure and rupture. Most of the time initiation of stress corrosion cracking (SCC) and pitting corrosion are detected by coincidence in excavation and digs and is not targeted or predicted by analysis of corrosion performance parameters. Internal or In-line inspection (ILI) tools have limited capability for detecting or identifying stress corrosion cracking and pitting corrosion initiation. Here we would like to elaborate on corrosion risk assessment based on soil corrosivity mapping in addition to procedures outlined in NACE SP 0204-2015.
Keywords: Stress Corrosion Cracking (SCC), Pitting Corrosion, Corrosion Risk Assessment, Soil Resistivity, Soil Corrosivity Mapping, Coating Disbondment and Cathodic Protection.
- A Distributed Analytical Electro-thermal Model for Pouch-type Lithium-ion Batteries, Journal of The Electrochemical Society, Vol. 161, A1953-A1963 (2014).
- A Computationally-effective Thermal Model for Spirally Wound Nickel-metal Hydride Batteries, Journal of The Electrochemical Society, Vol. 161, A109-A117 (2014).
- Analytical Assessment of the Thermal Behavior of Nickel-metal Hydride Batteries During Fast Charging, Journal of Power Sources, Vol. 245, pp. 712−720 (2014).
- Electrical Constriction Resistance in Current Collectors of Large-scale Lithium-ion Batteries, Journal of The Electrochemical Society, Vol. 160, A1731-A1740 (2013).
- Transient Three-dimensional Thermal Model for Batteries with Thin Electrodes, Journal of Power Sources, Vol. 243, pp. 280−289 (2013).
- Temperature Rise in Prismatic Polymer Lithium-ion Batteries: An Analytic Approach, SAE International Journal of Passenger Cars – Electronic and Electrical Systems, Vol. 5, pp. 164−176 (2012).
- Investigating Electrical Contact Resistance Losses in Lithium-ion Battery Assemblies for Hybrid and Electric Vehicles, Journal of Power Sources, Vol. 196, pp. 6525−6533 (2011).